The present invention relates to an improved screen filter device or strainer which is used in separating a mixture for recovering the solids, cleaning the liquid and/or thickening the liquid.
There presently exists in many industries, particularly the papermaking industry, the need to separate solids from liquids. In this regard, filtering of the liquid provides for a convenient way of providing same. Heretofore as set forth in U.S. Pat. No. 3,112,263 a screen filter device is shown where a cleansing spray of liquid is used to clean the screen of the filter of solids and other debris. The liquid is sprayed upward and impinges upon the screen passing therethrough to provide a cleansing effect. Improvements thereon include U.S. Pat. No. 4,412,920, the disclosure of which is incorporated herein by reference, wherein a filtering device is disclosed. This device utilizes a screen having a central opening and a top spray arranged so that the liquid to be filtered flows through the screen. The solids collected are forced along the screen toward a central opening. Thus the separation of the solids from the liquid occurs.
An improvement upon that device is that set forth in U.S. Pat. No. 5,259,955, the disclosure of which is also incorporated herein by reference. In this latter patent, the performance of the strainer is improved significantly through the application of a vacuum under the screen thereby applying an additional force on the liquid being strained to force it through the screen. To prevent stapling, a high pressure cleansing fluid is directed at the screen at the same time at an angle with the nominal plane or surface of the screen to force the solids strained by the screen to roll towards the center opening before the solids become stapled. A further improvement upon the foregoing is that disclosed in U.S. Pat. No. 5,453,193. The device disclosed therein includes two concentric containers, the outer one feeling a solid/liquid mixture to the inner container and the inner container supporting a screen. The mixture flows onto the screen so that the liquid goes through the screen and the solids, assisted by a shower action, roll toward a central opening. To insure that the mixture flows evenly onto the screen, a weir structure is provided.
In many of the strainers, particularly those used in the papermaking industry, a replaceable filter media is used which is maintained on a support structure. Typically the support structure includes a reject opening in the center. See for example U.S. Pat. No. 4,412,920, elements 24 (which is the screen and support structure as one element) and 26.
Replacement of the filter media is a required routine maintenance procedure, since the media after time either becomes too clogged to be efficient or otherwise wears out. This is usually an expensive, difficult and time consuming procedure. Typically, what is involved is removing the old filter media and stretching the new filter media into position and clamping it in place between steel rings. This requires that the strainer be shut down, the filter media removed, disassembled with the new filter media stretched evenly and clamped by way of a multiplicity of fasteners. The reject opening is also clamped and the refitted filter assembly is then placed back in the strainer vessel and reassembled.
Thus it can be appreciated that it would be advantageous to simplify the filter replacement process.
It is therefore a principal object of the invention to provide for a strainer that overcomes the problems and difficulties in replacing filter media in strainers.
It is further object to provide for a replacement filter media which is readily implemented without requiring disassembly and re-assembly of the strainer.
A yet further object is to provide for a replacement filter media which is easily and accurately tensioned for proper use.
Such objects are achieved by the present invention which is directed to a filter media made of fabric which includes a tensioning member around its circumference so as to evenly tension the media over a support structure. An axially positioned reject opening and skirt is also provided. Such an arrangement may be readily assembled and replaced in the strainer avoiding the disadvantages heretofore encountered.